Hydraulic diameter conversion of runners in plastic mold gating system design
Hydraulic diameter refers to 4 times the ratio of the flow cross-sectional area to the perimeter, as the wall shear stress of non-circular pipes is not even distributed along the surrounding walls, only the average value of the surrounding walls can be calculated.
The main cross-sectional shapes of the shunt: round, trapezoidal and rectangular, in order to reduce the pressure heat loss in the runner, the cross-sectional area of the runner should be maximized, and the internal surface area for heat dissipation should be the smallest.
The efficiency of the runner is expressed by the ratio of the cross-sectional area S of the runner to its cross-sectional circumference L.
Splitter efficiency (hydraulic radius) n=cross-sectional area/cross-sectional circumference=S/L
Hydraulic diameter=4n=4S/L
From the above information, we can see the flow efficiency of different cross-section runners, round and trapezoidal cross-sections are the preferred runners. The size of the runner is usually selected based on the diameter of the circular runner (equal to the hydraulic diameter); when other cross-section flow channels are used, the hydraulic diameter must be converted so that the flow efficiency can meet the calculation requirements (see the example below) ).
Example: It is calculated that a product needs a 8m hydraulic diameter runner, and a semicircular runner is now used; what size of semicircle is more reasonable?
Hydraulic diameter=4n=4S/L=(4*(πr²)/2)/(π*r+2r)=8
Radius r=8*(π+2)/(2π)=6.55
Diameter D=2*r=6.55*2=13.1
Answer: A semicircular runner with a diameter of about 13m is more suitable.
Different treatment of plastic injection mold cooling system principles
Feb 22, 2022Different treatment principle: 1. The mold temperature is different according to the different plastics, when the plastic requires the molding temperature of the mold to be ≥80°C, the mold must be...viewPin-point gate of plastic injection mold runner system design
Jan 24, 2022In order to get the best injection quality, the gate type must be selected carefully, the coommon gate tyeps are: direct gate, side gate, pin-point gate, sub gate,valve gate of hot runner etc. Among...viewThe design requirements of slider wear plate
Jan 2, 20241. The wear plate of slider requires hardening treatment, with a hardness of 45-48HRC; 2. The friction surface of the wear plate is required to be 1.0mm higher than the slider surface (see picture-1);...viewDesign principles for wall thickness of plastic products
Jan 3, 2022The principles of wall thickness design for plastic parts are as follows: 1. Making the wall thickness even is the first principle of plastic part design, it can make filling, cooling and shrinking...viewDesign principles of plastic injection mold runner system
Jan 6, 20221. Quality first The design of the gating system has a big influence on part quality, firstly the gate should be set at the easiest part of the plastic part to be removed, and at the same time, the...viewPlastic injection mold runner system design points
Jan 9, 2022When designing the gating system, Firstly, we should consider making the plastic melt fill the cavity with core side quickly to reduce pressure and heat loss; secondly, it should be economically...view